One serious problem encountered in vehicles using fossil fuels such as gasoline or light oil is air pollution. As a measure to solve such a problem, a technology for using re-chargeable secondary cells as a power source for vehicles is receiving attention. Thus, an electric vehicle (EV), which can be driven only using a battery, a hybrid electric vehicle (HEV), which uses a battery in combination with a conventional combustion engine, or the like has been developed, and is commercially available. For secondary cells as a power source of EVs, HEVs, or the like, nickel metal hydride (Ni-MH) cells are mainly used. Recently, use of lithium ion cells has also been attempted.
In order to be used as a power source of EVs, HEVs, or the like, the cells should have high power and large capacity. To this end, a medium or large cell pack having a structure, in which a plurality of small secondary cells (unit cells) is connected in series and/or in parallel, is used.
Since unit cells, which are constituent elements of the medium or large cell pack, are stacked at high density, a prismatic cell or a pouch type cell, which is capable of reducing the size of a dead space, is used as such a unit cell. In order to achieve easy mechanical fastening and easy electrical connection of unit cells as mentioned above, a battery cartridge capable of mounting one unit cell or two or more unit cells is generally used. That is, a plurality of battery cartridges, in which unit cells are mounted, is stacked to form a cell pack.
Such battery cartridges require protection, insulation, and heat dissipation of internal unit cells thereof. Also, free stacking and configuration of battery cartridges are required.